Writing syntax-propertize-function for strings in code in strings, etc

[Dmitry Gutov <dgutov@yandex.ru>]

Hi all,

I've been looking into this bug: http://bugs.ruby-lang.org/issues/6090

To elaborate, Ruby allows arbitrary code between string interpolation
braces, and even unlimited nesting of those.

Sublime Text handles these aspects rather excellently, and even
highlights the code inside as code, not string contents:
http://i.imgur.com/NH1Ye.png

Is there a proper way to do so in Emacs?

My first idea was, when propertizing interpolation, to see what kind of
string we're inside, and apply the appropriate syntax to the enclosing
braces, thus splitting the literal in two.  But (a) string quotes class
doesn't work that way (text characters on both ends of a literal must
be the same), (b) if we're inside a percent literal (syntax class:
generic string), and the literal spans several lines, we need to be able
to jump to its real beginning position from its end, but with this
approach (nth 8 (syntax-ppss)) will just return the beginning of the
last piece.  Saving buffer positions to text properties looks not very
reliable, since the respective text may be deleted and re-inserted.

Suggestions?

A quick and dirty way is to limit the support to double-quoted strings,
no change in highlighting, and no nesting, but that would be the last
resort.

--Dmitry